Why new MySqlParameter (& quot; @ val & quot;, 0). Value =

Some time ago, when my colleagues wrote code, they found that MySQL Data Tables were often inserted with magical null values. After tracking the code for half a day, they finally found the problem:

 
 

  
  
DbParameter p = new MySqlParameter ("@ val", 0 );
  
  
Debug. Assert (p. Value = 0); // Assert fails. p. Value is actually null.
 
 

After analysis for half a day, no reason was found. I guess MySql. Data treats 0 as null. I thought, it shouldn't be. There's no reason at all. What a normal value 0 is in the database! So I downloaded the source code of MySql. Data for debugging and tracking ...... Then I found a terrible thing.

MySqlParameter has several BUILD functions, two of which are stated in this statement.

 
 

  
  
Public MySqlParameter (string name, object value ){
  
  
//......
  
  
}
  
  
 
  
  
Public MySqlParameter (string name, MySqlDbType ){
  
  
//......
  
  
// MySqlDbType is an enumeration type.
  
  
}
 
 

P = new MySqlParameter ("@ val", 0) actually calls the second build function. 0 is converted to MySqlDbType. decimal is passed in, and no Value is assigned for its Value. Of course, p. the Value is null.

Then, will not all input integers be treated as enumeration ...... Otherwise, if the input value is not 0, the call is the first build function, and 1 is processed as an object!

Then I am wondering why 0 will be automatically converted to the enumeration type for processing, rather than 0 will be treated as an object? Why? Who can tell me the answer?

The problem is solved ......

 
 

  
  
DbParameter p = new MySqlParameter ("@ val", (object) 0 );
  
  
Debug. Assert (p. Value = 0); // Assert successful
 
 

 

This article from the "Edge City inn xuehai Wuxi" blog, please be sure to keep this source http://jamesfancy.blog.51cto.com/2516291/1162445